In electron beam melting installations and in electron beam vaporization installations the problem is encountered that electron beams with relatively large cross-sectional areas must remain bundled over a relatively great distance. Imaging errors here have a significantly stronger effect than for example in television tubes in which relatively short distances are overcome with a very thin electron beam. Moreover, in melting and vaporization installations high vapor deposition rates occur whereby the inner walls of deflection units are very quickly covered with, most frequently, a metallic process material. In the hereby ongrowing metal layers, eddy currents occur if they are penetrated by a magnetic deflection field which is variable in time. These eddy current losses increase with the area permeated by the field, which necessitates a deflection system of minimum possible size.
An electron beam melting installation is already known per U.S. Pat. No. 4,988,844, in which a cylindrical metal ingot is disposed above a tub and its lower end is melted off by two electron beams. However, in this patent there is not shown how the deflection of the electron beams is specifically carried out.
The same is true for another installation comprising a single electron beam capable of being deflected (German Patent No. 35 32 888).
Further it is known to treat material in a vaporization crucible by means of an electron beam which can be deflected by magnet coils (German published patent application No. 35 13 546), with deflection coils that are ring-shaped and include a cylindrical deflection channel.
In another known arrangement for generating metal ingots by means of electron beams a cylindrical metal ingot is melted off at its lower end of two obliquely incident electron beams (U.S. Pat. No. 3,219,435). The regulation of the electron beams takes place through focusing devices, a mechanical diaphragm, and a deflection coil, and the deflection coil is implemented in the form of a circular arc.
In television applications, thick-neck tubes with saddle coils are used for the realization of 110.degree. deflection of electron beams (B.Morgenstein, Farbfernsehtechnik, 1977, p. 58 to 60; P. Zastrow, Fernsehempfangstechnik, 1978, p. 146). Focusing in the case of such tubes most often takes place magnetically.
In general, torodal coils are used for vertical deflection while horizontal deflection coils are implemented as saddle coils with relatively large coil length.
Such deflection systems, however, are not suitable for high-power electron beams because they are only capable of deflecting precisely thin electron beams close to the axis, but not electron beams with large cross-sectional areas.
Further, an electron scan microscope is known, in which an electron beam is bundled and deflected to a sample (German Patent No. 31 45 606). Upper and lower deflection coils are provided, the lower deflection coil being saddle-shaped. However, the deflection coils cannot be used for deflecting high-power electron beams having extensive cross-sectional areas.
Finally, a magnetic scanning system is known wherein ions are deflected (European published patent application No. 0 473 097). However, the coils used with this system are ring-shaped.